Cutter inserts commonly employ a plurality of lateral faces or sides and cutting edges whereby the cutting edges may be sequentially utilized as the tool wears. In common constructions such cutting inserts are often triangular in configuration having three lateral sides and cutting edges, or the cutting inserts may commonly be formed of a square configuration utilizing four similar cutting edges. Typical examples of cutter inserts of the above type are shown in U.S. Pat. Nos. 3,097,417; 3,137,918; 3,395,434; 3,781,956; 3,786,541 and 3,815,191.
As the length of the lateral sides of cutter inserts such as those disclosed in the above patents are equal, inserts utilizing three sides define an apex of 60.degree. as formed by intersecting lateral sides, while four sided cutter inserts have 90.degree. corners as defined by intersecting lateral sides.
The corner edges of conventional cutter inserts often break during use in that the 60.degree. and 90.degree. included angles defined by the inserts intersecting lateral sides do not provide sufficient support of the material defining the cutting edge at the corner, and fracture often occurs at the corners of the insert requiring the replacement of the insert lateral side and cutting edge by rotating the insert upon its support.
Patents such as those identified above also utilize chip forming recesses adjacent the cutting edge. Such recesses are normally of an elongated concave configuration which cause the chip to be deflected upwardly after being removed from the workpiece. This deflection of the chip will tend to shape the chip, and cause a curl which aids in removing the chip from the cutting area. U.S. Pat. No. 3,815,191 is particularly directed to chip formation.
Because of the radius that occurs at the corners of conventional cutter inserts the configuration of the chip recess is such that the flow of the chip at the corner is not parallel with the chip flow at the linear portions of the cutting edge, and such non-parallel movement of the chip causes chip interference within the recess and may result in chip entanglement and "balling". Further, such non-parallel flow of the chip adjacent the insert corner substantially increases the power required to remove the chip and will result in insert "hot spots" which accelerate wear.